Class ShingleFilter

A ShingleFilter constructs shingles (token n-grams) from a token stream. In other words, it creates combinations of tokens as a single token.

For example, the sentence "please divide this sentence into shingles" might be tokenized into shingles "please divide", "divide this", "this sentence", "sentence into", and "into shingles".

This filter handles position increments > 1 by inserting filler tokens (tokens with termtext "_"). It does not handle a position increment of 0.

Inheritance

object

AttributeSource

TokenStream

TokenFilter

ShingleFilter

Implements

IDisposable

Inherited Members

TokenStream.Dispose()

AttributeSource.GetAttributeFactory()

AttributeSource.GetAttributeClassesEnumerator()

AttributeSource.GetAttributeImplsEnumerator()

AttributeSource.AddAttributeImpl(Attribute)

AttributeSource.AddAttribute<T>()

AttributeSource.HasAttributes

AttributeSource.HasAttribute<T>()

AttributeSource.GetAttribute<T>()

AttributeSource.ClearAttributes()

AttributeSource.CaptureState()

AttributeSource.RestoreState(AttributeSource.State)

AttributeSource.GetHashCode()

AttributeSource.Equals(object)

AttributeSource.ReflectAsString(bool)

AttributeSource.ReflectWith(IAttributeReflector)

AttributeSource.CloneAttributes()

AttributeSource.CopyTo(AttributeSource)

AttributeSource.ToString()

object.Equals(object, object)

object.GetType()

object.ReferenceEquals(object, object)

Namespace: Lucene.Net.Analysis.Shingle

Assembly: Lucene.Net.Analysis.Common.dll

Syntax

public sealed class ShingleFilter : TokenFilter, IDisposable

Constructors

ShingleFilter(TokenStream)

Construct a ShingleFilter with default shingle size: 2.

Declaration

public ShingleFilter(TokenStream input)

Parameters

Type	Name	Description
TokenStream	input	input stream

ShingleFilter(TokenStream, int)

Constructs a ShingleFilter with the specified shingle size from the Lucene.Net.Analysis.TokenStreaminput

Declaration

public ShingleFilter(TokenStream input, int maxShingleSize)

Parameters

Type	Name	Description
TokenStream	input	input stream
int	maxShingleSize	maximum shingle size produced by the filter.

ShingleFilter(TokenStream, int, int)

Constructs a ShingleFilter with the specified shingle size from the Lucene.Net.Analysis.TokenStreaminput

Declaration

public ShingleFilter(TokenStream input, int minShingleSize, int maxShingleSize)

Parameters

Type	Name	Description
TokenStream	input	input stream
int	minShingleSize	minimum shingle size produced by the filter.
int	maxShingleSize	maximum shingle size produced by the filter.

ShingleFilter(TokenStream, string)

Construct a ShingleFilter with the specified token type for shingle tokens and the default shingle size: 2

Declaration

public ShingleFilter(TokenStream input, string tokenType)

Parameters

Type	Name	Description
TokenStream	input	input stream
string	tokenType	token type for shingle tokens

Fields

DEFAULT_FILLER_TOKEN

filler token for when positionIncrement is more than 1

Declaration

public const string DEFAULT_FILLER_TOKEN = "_"

Field Value

Type	Description
string

DEFAULT_MAX_SHINGLE_SIZE

default maximum shingle size is 2.

Declaration

public const int DEFAULT_MAX_SHINGLE_SIZE = 2

Field Value

Type	Description
int

DEFAULT_MIN_SHINGLE_SIZE

default minimum shingle size is 2.

Declaration

public const int DEFAULT_MIN_SHINGLE_SIZE = 2

Field Value

Type	Description
int

DEFAULT_TOKEN_SEPARATOR

The default string to use when joining adjacent tokens to form a shingle

Declaration

public const string DEFAULT_TOKEN_SEPARATOR = " "

Field Value

Type	Description
string

DEFAULT_TOKEN_TYPE

default token type attribute value is "shingle"

Declaration

public const string DEFAULT_TOKEN_TYPE = "shingle"

Field Value

Type	Description
string

Methods

End()

This method is called by the consumer after the last token has been consumed, after Lucene.Net.Analysis.TokenStream.IncrementToken() returned false (using the new Lucene.Net.Analysis.TokenStream API). Streams implementing the old API should upgrade to use this feature.

This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

NOTE: The default implementation chains the call to the input TokenStream, so be sure to call base.End() first when overriding this method.

Declaration

public override void End()

Overrides

Lucene.Net.Analysis.TokenFilter.End()

Exceptions

Type	Condition
IOException	If an I/O error occurs

IncrementToken()

Consumers (i.e., Lucene.Net.Index.IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate Lucene.Net.Util.IAttributes with the attributes of the next token.

The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use Lucene.Net.Util.AttributeSource.CaptureState() to create a copy of the current attribute state.

this method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to Lucene.Net.Util.AttributeSource.AddAttribute<T>() and Lucene.Net.Util.AttributeSource.GetAttribute<T>(), references to all Lucene.Net.Util.IAttributes that this stream uses should be retrieved during instantiation.

To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in Lucene.Net.Analysis.TokenStream.IncrementToken().

Declaration

public override bool IncrementToken()

Returns

Type	Description
bool	false for end of stream; true otherwise

Overrides

Lucene.Net.Analysis.TokenStream.IncrementToken()

Reset()

This method is called by a consumer before it begins consumption using Lucene.Net.Analysis.TokenStream.IncrementToken().

Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

If you override this method, always call base.Reset(), otherwise some internal state will not be correctly reset (e.g., Lucene.Net.Analysis.Tokenizer will throw InvalidOperationException on further usage).

Declaration

public override void Reset()

Overrides

Lucene.Net.Analysis.TokenFilter.Reset()

Remarks

NOTE: The default implementation chains the call to the input Lucene.Net.Analysis.TokenStream, so be sure to call base.Reset() when overriding this method.

SetFillerToken(string)

Sets the string to insert for each position at which there is no token (i.e., when position increment is greater than one).

Declaration

public void SetFillerToken(string fillerToken)

Parameters

Type	Name	Description
string	fillerToken	string to insert at each position where there is no token

SetMaxShingleSize(int)

Set the max shingle size (default: 2)

Declaration

public void SetMaxShingleSize(int maxShingleSize)

Parameters

Type	Name	Description
int	maxShingleSize	max size of output shingles

SetMinShingleSize(int)

Set the min shingle size (default: 2).

This method requires that the passed in minShingleSize is not greater than maxShingleSize, so make sure that maxShingleSize is set before calling this method.

The unigram output option is independent of the min shingle size.

Declaration

public void SetMinShingleSize(int minShingleSize)

Parameters

Type	Name	Description
int	minShingleSize	min size of output shingles

SetOutputUnigrams(bool)

Shall the output stream contain the input tokens (unigrams) as well as shingles? (default: true.)

Declaration

public void SetOutputUnigrams(bool outputUnigrams)

Parameters

Type	Name	Description
bool	outputUnigrams	Whether or not the output stream shall contain the input tokens (unigrams)

SetOutputUnigramsIfNoShingles(bool)

Shall we override the behavior of outputUnigrams==false for those times when no shingles are available (because there are fewer than minShingleSize tokens in the input stream)? (default: false.)

Note that if outputUnigrams==true, then unigrams are always output, regardless of whether any shingles are available.

Declaration

public void SetOutputUnigramsIfNoShingles(bool outputUnigramsIfNoShingles)

Parameters

Type	Name	Description
bool	outputUnigramsIfNoShingles	Whether or not to output a single unigram when no shingles are available.

SetTokenSeparator(string)

Sets the string to use when joining adjacent tokens to form a shingle

Declaration

public void SetTokenSeparator(string tokenSeparator)

Parameters

Type	Name	Description
string	tokenSeparator	used to separate input stream tokens in output shingles

SetTokenType(string)

Set the type of the shingle tokens produced by this filter. (default: "shingle")

Declaration

public void SetTokenType(string tokenType)

Parameters

Type	Name	Description
string	tokenType	token tokenType

Implements

IDisposable